Functionalized, water-soluble polymers are well known in the art and are useful in a variety of applications. A major drawback of many functionalized polymers is their tendency to cross-link, this problem becoming more severe as the polymer solids content or the molecular weights thereof is increased. Attempts to reduce the tendency of such polymers to cross-link have proven less than satisfactory.
For example, high molecular weight Mannich acrylamide polymers (PAMS) are well known and are used in a variety of flocculant applications. A major drawback of Mannich PAMS is their tendency to cross-link. This problem becomes more severe as the polymer solids are increased. Consequently, these polymers are generally made as dilute aqueous solutions in an attempt to slow dow the rate of interpolymer cross-linking. The solids level must also be kept low, particularly for very high molecular weight Mannich PAMS, owing to the ability of these polymers to viscosify water. As a result, solids levels of very high molecular weight Mannich PAMS must generally be well below 10%, and more typically 6% or less so that the solutions can be pumped and handled conveniently.
Several approaches have been tried to overcome these problems. One approach has been to make the Mannich PAMS at the site of use by inverting high solids inverse emulsion PAMS in water containing dialkylamines and formaldehyde. U.S. Pat. Nos. 4,021,394 and 4,022,741 describe continuous processes for the preparation of Mannich PAMS which entails inverting an inverse emulsion PAM in a process stream containing formaldehyde and a secondary amine and subjecting the stream to turbulence by in-line mixing to produce an 1-15% aqueous solution of Mannich PAM. This approach, however, suffers from the need to store multiple chemicals on site and from the problems inherent in running chemical reactions at such locations. Another approach has been to prepare dry Mannich PAMS, as described in U.S. Pat. Nos. 3,864,312; 3,539,535 and 3,790,529, or blends of dry PAMS with dry, low-molecular weight Mannich-base forming compounds which, when dissolved in water, react to produce Mannich PAMS, as described in EPO No. 210,784. These approaches, in general, suffer from cross-linking problems, the reversibility of the Mannich reaction, the difficulty and length of time required to dissolve high molecular weight polymers, and other problems. Another approach has been to make the Mannich PAM in inverse emulsions, such as described in U.S. Pat. Nos. 3,979,348, 4,093,542 and 4,010,131. While this approach produces a product with substantially higher solids, the average particle size thereof ranges from 10,000-20,000 .ANG. in diameter, and consequently, cross-linking of the thousands of polymer chains in each particle renders the products ineffective. The cross-linking rate can be reduce somewhat by adding fairly large quantities of stabilizers such as described in U.S. Pat. Nos. 4,113,685 and 4,073,763, but cross-linking continues and the products thus possess a very limited shelf life.
Water-soluble, glyoxalated acrylamide polymer wet strength agents are disclosed in Coscia, U.S. Pat. No. 3,556,932, incorporated herein by reference. These wet-strength agents are made from polymers with molecular weights ranging from less than about 1,000,000 preferably less than about 25,000. The polymers are reacted with glyoxal in a dilute, aqueous solution to impart --CONHCHOHCHO functionalities onto the polymer and to increase the molecular weight of the polymer through glyoxal cross-links. Low molecular weight polymers and dilute solutions are required to impart at least a 6 percent --CONHCHOHCHO functionality to the polymers without infinitely cross-linking, or gelling, them in which condition the polymers are useless for wet-strength applications. Even at these low solids concentrations (dilute conditions), cross-linking continues and limits the shelf life of the product. For example, commercial products, supplied as 10% solids solutions, gel within about 8 days at room temperature.
Another class of water-soluble polymers which suffers from intermolecular cross-linking problems is the epoxide-substituted amine containing wet-strength polymers, such as those disclosed in U.S. Pat. No. 4,233,417 (incorporated herein by reference) and references contained therein. These functionalized polymers are well known to cross-link rapidly by the reaction between the polymer amine and epoxide or chlorohydrin groups, yielding gels which do not perform. To lessen the extent of the problem, several approaches have been taken including diluting the products after manufacture, adjusting the pH to deactivate the epoxide functional groups and reacting the polymeric amines with excess epichlorohydrin to completely quaternize and deactivate all amine groups. These approaches suffer from reduced active solids content of the product, increased processing costs, increased epichlorohydrin requirements and the like.
Other products, produced from various functional group containing materials, discussed more fully hereinbelow, also suffer from the problem of cross-linking and the attendant utility deficiencies and these, also, fall within the scope of products possessing use problems which may be alleviated by this invention.
Accordingly, there exists a need for functionalized water-soluble polymers which can be prepared at high solids levels or at high molecular weight without extensive interpolymer cross-linking such that they may be economically transported and easily handled by the end user without the need for any on site preparation. Such functionalized polymers would satisfy a long felt need and constitute a notable advance in the state of the art.
Surprisingly, it has now been discovered, that functioalized, water-soluble, polymer-based, polymer particles in the form of inverse emulsions or microemulsions can be prepared which polymer particles exhibit performance characteristics superior to those of the prior art as cross-linking occurs. In contrast to prior art methods of production wherein the functionalized polymers contain large quantities of polymer molecules in the same aqueous environment, the functionalized polymers of the present invention are isolated as individual, or a limited number of polymer molecules in each aqueous emulsion micelle. Thus, the problem of large scale interpolymer crosslinking inherent in the solution and inverse emulsion products of the prior art is overcome resulting in polymers which, even though cross-linked, are useful for their intended purpose.